regarding a large codebase needing good java inter...

# codingconventions

[groostav]

regarding a large codebase needing good java interop, thoughts on the function signature

class ConvertedOldModelObject private constructor(oldCtorArg: OldJavaDomainType, ...) {
  //...
  companion object {
    @JvmStatic @JvmName("create") operator fun invoke(oldCtorArg: OldJavaDomainType, ...) {
      //some caching logic to try to avoid hanging on to allocaitons, a kind of poor mans constant pool

      return CovertedOldModelObject(oldCtorArg, cachedArgs, ...)
    }
  }
}

pros:
• I get OldJavaDomainType oldThing = OldJavaDomainType.create(args...) from java
• I get val x = OldJavaDomainType(args...) from kotlin
cons:
• companion object operator fun invoke seems like a kind of nifty hack, not sure how somebody else would feel stumbling across it
• reasonable alternatives like simply offering a global function for kotlin and a simpler fun create() method for java seems sufficient, though slightly bloatier

[ephemient]

pooling is generally a bad idea in modern JVMs (and even Android ART)

[ephemient]

any sort of thread safety will be slower than simply getting new objects from the bump allocator and letting GC clean them up

[ephemient]

as for the API itself, the companion object { operator invoke() } trick is fine. overall I think it's more common in Kotlin to use

interface Foo
private class FooImpl(...) : Foo
public fun Foo(...): Foo = FooImpl(...)

but that doesn't lead to the same Java API

[Youssef Shoaib [MOD]]

companion object operator fun invoke is definitely idiomatic Kotlin, but yes sometimes people just have a top-level function with the class name. Personally, I think here it makes the most sense to use a companion object so that you get the wanted experience from Java